This invention relates to a process for producing a carboxylic acid which comprises reacting a hydrocarbyl alcohol with carbon monoxide.
A process for producing a carboxylic acid by carbonylation reaction of an alcohol, such as a process for producing acetic acid from methanol and carbon monoxide was known.
In the prior art, the known catalysts for producing carboxylic acids from alcohols and carbon monoxide include the following:
(i) a catalyst comprising a noble metal belonging to Group VIII of the Periodic Table, such as rhodium, a halide and a third component as disclosed in Japanese Patent Publication (Kohkoku) Nos. 3331/1972; 3332/1972; 3333/1972; 3334/1972; 3335/1972; 3336/1972 and 3337/1972, and
(ii) a catalyst comprising nickel or cobalt, halide and a third component as disclosed in U.S. Pat. Nos. 2,729,651; 2,727,902 and 4,134,912 and German Pat. Nos. 921,938; 933,148 and 947,469, Japanese Patent Publication (Kohkai) No. 84912/1978 and Japanese Patent Publication (Kohkai) Nos. 59211/1979; 63002/1979 and 66614/1979 assigned to the assignee of this invention.
However, catalyst (i) contains expensive rhodium as shown in Hydrocarbon Processing 54, June 83 (1975).
In case of producing carboxylic acids from hydrocarbyl alcohols and carbon monoxide by using a rhodium catalyst, a rhodium complex has to be prevented from being reduced to metallic rhodium under a reducing atmosphere as disclosed in KAKTAF 29 (5) page 376 (1975) or the rhodium component has to be prevented from being scattered from the reaction system during the operation of separating the product as disclosed in Japanese Patent Publication (Kohkai) No. 99204/1978.
The method using component (ii), such as described in U.S. Pat. No. 4,134,912 and Japanese Patent Publication (Kohkai) No. 84912/1978, is attractive in that it uses an inexpensive nickel catalyst, but in this method, as much as about 40% of an iodide cocatalyst is present in the reaction system. Further, the method requires a large amount of ligand typified by triphenylphosphine, but no corresponding improvement in the yield of the reaction product and reaction rate is achieved. As another disadvantage, the ligand used in a large amount is sparingly soluble in the reaction liquor and recycling of the catalyst and cocatalyst that is necessary in continuous operation is very difficult, if not impossible. At the same time, the ligand is labile and its activity is rapidly reduced. For these reasons, the second method has not been used on an industrial scale.